# [Pw_forum] Example7

Amit Kumar amit76.india at gmail.com
Tue Mar 6 07:29:00 CET 2007

```   Respected Users,

I'm very much confused with the Electron-phonon output of Example 7.
Please check it out:

1 .  KPOINT  16 16 16 for scf.fit    and   2 2 2 for scf calculation.

Gaussian Broadening:   0.090 Ry, ngauss=   0
DOS =  2.674745 states/spin/Ry/Unit Cell at Ef=  8.266810 eV
lambda( 1)=  0.1373   gamma=   15.97 GHz
lambda( 2)=  0.1116   gamma=   12.97 GHz
lambda( 3)=  0.0504   gamma=    6.93 GHz

Gaussian Broadening:   0.10 Ry, ngauss=   0
DOS =  2.674314 states/spin/Ry/Unit Cell at Ef=  8.266772 eV
lambda( 1)=  0.1403   gamma=   16.32 GHz
lambda( 2)=  0.1132   gamma=   13.16 GHz
lambda( 3)=  0.0520   gamma=    7.15 GHz

2.   KPOINT  16 16 16 for scf.fit    and   8 8 8 for scf calculation.

Gaussian Broadening:   0.090 Ry,       ngauss=   0
DOS =  2.673746 states/spin/Ry/Unit Cell at Ef=  8.271433 eV
lambda( 1)=  0.0828   gamma=    8.96 GHz
lambda( 2)=  0.1720   gamma=   26.90 GHz
lambda( 3)=  0.1742   gamma=   27.24 GHz

Gaussian Broadening:   0.10 Ry, ngauss=   0
DOS =  2.674314 states/spin/Ry/Unit Cell at Ef=  8.266772 eV
lambda( 1)=  0.0831   gamma=    8.99 GHz
lambda( 2)=  0.1721   gamma=   26.93 GHz
lambda( 3)=  0.1740   gamma=   27.22 GHz

So I thought great I got  convergency so easily.
lambda( 2)=  0.1720   gamma=   26.90 GHz
lambda( 3)=  0.1742   gamma=   27.24 GHz

and

lambda( 2)=  0.1721   gamma=   26.93 GHz
lambda( 3)=  0.1740   gamma=   27.22 GHz

Very excellent results.

But. life is not  so simple. Bad luck.
With even  more K points again results start to become worse instead of
being better.

Please check it out :

3.   KPOINT  32 32 32  for scf.fit    and   16 16 16  for scf
calculation.

Gaussian Broadening:   0.090 Ry,       ngauss=   0
DOS =  2.675256 states/spin/Ry/Unit Cell at Ef=  8.271367 eV
lambda( 1)=  0.0799   gamma=    9.12 GHz
lambda( 2)=  0.1703   gamma=   28.62 GHz
lambda( 3)=  0.1705   gamma=   28.64 GHz

Gaussian Broadening:   0.10 Ry,       ngauss=   0
DOS =  2.674732 states/spin/Ry/Unit Cell at Ef=  8.266803 eV
lambda( 1)=  0.0799   gamma=    9.12 GHz
lambda( 2)=  0.1686   gamma=   28.32 GHz
lambda( 3)=  0.1687   gamma=   28.34 GHz

4.    KPOINT  64 64 64   for scf.fit    and   32 32 32   for scf
calculation.

Gaussian Broadening:   0.090 Ry,       ngauss=   0
DOS =  2.675273 states/spin/Ry/Unit Cell at Ef=  8.271375 eV
lambda( 1)=  0.0801   gamma=    9.07 GHz
lambda( 2)=  0.1726   gamma=   28.29 GHz
lambda( 3)=  0.1726   gamma=   28.29 GHz

Gaussian Broadening:   0.10 Ry,       ngauss=   0
DOS =  2.674745 states/spin/Ry/Unit Cell at Ef=  8.266810 eV
lambda( 1)=  0.0802   gamma=    9.08 GHz
lambda( 2)=  0.1708   gamma=   27.99 GHz
lambda( 3)=  0.1708   gamma=   27.99 GHz

Would anybody tell me the reason,  Why the case (2)    ( for magic
number
KPOINT  16 16 16 for scf.fit    and   8 8 8 for scf calculation)
is  so kind
to us?????? How far we will go to get the converged value???
Where can we stop????
It's really confusing.

Looking forward to your help.

Regards,
Amit
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